Field of the Invention
The present invention relates to a method of controlling a continuously variable valve timing system for limp-home. More particularly, the present invention relates to a method of controlling an intermediate phase continuously variable valve timing system for limp-home of a CVVT system.
Description of Related Art
Generally, a continuously variable valve timing (CVVT) apparatus refers to an apparatus which adjusts opening and closing timing of a valve of an engine. Particularly, as the CVVT system controls an intake valve in accordance with a driving condition, output of the engine and fuel efficiency may be improved, and exhaust gas may be reduced.
The opening and closing operations of exhaust and intake valves are performed by a rotation of a camshaft, and a continuously variable valve timing system can control opening/closing timing of a valve by relative phase change of a camshaft.
A general CVVT system is a hydraulic vane type CVVT system. The vane type CVVT system is provided in a small space, and has a merit of being inexpensive.
However, because the vane type CVVT system uses lubricant of the engine as working oil, there is a drawback in that it is difficult to expect fast and accurate response in a state in which pressure of oil is low. Particularly, in a case in which pressure of engine oil is not sufficient, such as in an idle state of the engine, in a high temperature state, in a start state, or the like, a relative phase variation of the camshaft is difficult, and excessive leakage of exhaust gas may occur. In addition, by a shortfall of pressure of oil and excessive viscosity of oil at the time of cold starting, an operation of the hydraulic CVVT system may be impossible. Therefore, starting is performed at a parking position fixed by a lock pin.
Meanwhile, in case that a parking position fixed by the lock pin is a maximal advance or a maximal retardation, responsiveness may be deteriorated and area of operating a cam may be limited.
Recently, an intermediate phase CVVT system having a parking position which is not a maximal advance or a maximal retardation but an intermediate phase between them has developed to solve the problem. That is, if an intermediate phase continuously variable valve timing system is applied, responsiveness can be improved and area of operating a cam may be expanded.
However, when the control of the lock pin is not properly performed in a general technology electrically controlling the operation of the lock pin by a solenoid, problems such as impossibility of operating a CVVT system by malfunction of releasing the lock or oscillation of a cam by malfunction of parking the lock pin may be generated.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.